Decomposition of nitro-paraffins in jet propulsion motor operation



Aug. 7, 1962 zw c ET AL 3,048,007

' DECOMPOSITION OF NITRO-PARAFFINS IN JET PROPULSION MOTOR OPERATION Filed March 51, 1944 67 Fig- E W M a X INVENTORS FR/ 72 ZW/CKY FREDERICK J: w/ 5;

sited states Fatent @fhce 3,i8,@7 Patented Aug. 7, 1952 3,ll43,07 DECOMPQSETIUN @F NITRQ-PARAFFHNS 1N .l'ET PROPULSIQN MOTGR fliERATlQN Fritz Zwichy, Pasadena, and Frederick J. Ewing, Altadena, Calif assignors, by mesne assignments, to Aerojet-General orporation, Qincinnati, Ohio, a corporation of Ohio Filed Mar. 31, 1944, Ser. No. 528,893 Claims. (Q1. fill-$5.4)

This invention relates to jet propulsion motors and to methods and substances used in their operation. In particular it relates to jet propulsion motors employing as a propellant a single liquid fuel containing its own oxidizer, and to methods of improving the performance of such motors.

In the operation of jet propulsion motors, fuel is usually burned in a combustion chamber and the gas formed from the combustion is released at high velocity through an exhaust nozzle to create the propelling force. Nitroparafiins, and especially nitromethane or a mixture of nitrornethane with nitroethane, have been proposed in the copending application of Zwicky et al., Serial No. 526,- 064, filed March 11, 1944, now Patent No. 2,433,943, as a liquid fuel containing its own oxidizer. Decomposition of such a fuel may be accomplished by a catalyst within the motor, for example, a surface prepared from metal oxides.

Such catalytic surfaces, usually in the form of liners, sometimes tend to be brittle or friable and may require frequent replacement. According to our invention a catalyst may be added continuously to the motor during operation, thus insuring the constant presence of a sufiicient amount of catalyst to cause satisfactory auto-combustion of fuel.

Our invention may be carried out by injecting the catalyst into the motor in the form of a colloidal suspension in a fuel. For example, the finely divided catalyst may be mixed with ethyl alcohol or some similar non-detonating fuel, and injected into the motor through a small slush injector so as to intersect a spray of the fuel which is being injected into the motor.

An alternative way of carrying out the invention is to inject the catalyst into the motor in the form of a fluid or of a solution which will break down in the combustion chamber to give one or more catalytic substances.

The invention will be better understood from the following detailed description and the accompanying drawing in which:

FIG. 1 shows a jet thrust motor in cross section along its longitudinal axis;

FIG. 2 is an enlarged part view in cross section of the injector end of the motor shown in MG. 1; and

FIG. 3 is a part view in cross section of a motor having another type of injector.

Similar numerals refer to similar parts throughout the several views. r V

In FIG. 1 we show a jet motor which consists of a tubular combustion chamber 1 suitably threaded on both ends, having in its right hand end an exhaust nozzle 2 threadedly secured, which contains an opening 3 converging to a constricted portion 4 and diverging outwardly forming an exhaust opening 5. Near the opposite end of member l a spark plug 6 is inserted into its wall. In the opposite end of member 1 a plug-shaped member 7 is threadedly secured. Member 7 contains in its center portion an injector plug 8 secured by lock nut ll. The plug 8 has a flared tube connection 50 in its outside end and a concentric hole 9 terminating in an injection nozzle Iii. Injector plug 8 is made leakprof by an inserted O ring 12. There is provided an annular groove 13. Beginning at groove 13 a helical groove 14 is provided around the 2 injector plug and this helical groove terminates in a frusto conical end 15. End 15 is machined to forman annular frusto conical space 16 in the recess 17 of the member 7. Recess 17 has a concentric orifice I8 which permits a spray of fluid from concentric hole 9 to enter the combustion chamber 1.

Immediately below the screw plug 8 a tube connection 26 having a flared end 52 and a hole drilled through the center connecting with a hole 21 drilled to a blind stop, is secured by threads into member 7. Another hole 22 is provided which connects hole 21 and groove 13 of screw plug 8. Hole 22 is closed by plug 23 at the periphery of member 7. Immediately above injector plug 8 another tube connection 25 having a flared end 51 is screwed into member 7 A hole through the center of this connection joins with blind hole Q6. A smaller angular orifice 27 passes through member 7 from the end of orifice 26. Orifice 27 is so positioned that a fluid stream issuing from it intercepts the stream from injector 8.

In operation the liquid fuel, such as nitromethane or a mixture of nitromethane and nitroethane, is injected into the combustion chamber 1 through tube 30, hole 9 and nozzle iii of the injector plug 8. Simultaneously, a colloidal suspension of catalyst in a non-detonating fuel is injected, through tube 31, flared tube connection 2 1 holes 21 and 22 into groove 13 of injector plug 8 and through helix l4 and frusto conical space 16 into the combustion chamber l. The terms nitromethane and nitroethane as used in the present specification and claims, mean the mononitromethane and rnononiu'oethane respectively in accordance with the common usage of these words. Catalysts which may be conveniently used comprise iron oxide, chromium oxide, chromium hydroxide, cerium oxide, or mixtures thereof, or other metal oxides colloidally suspended in the non-detonating fuel which may, for example, be an alcohol. It is understood that this invention is not limited to the compounds listed above, but may be also used with other metal oxides catalytically active in the decomposition of suitable self-combustible fuels.

Dining initiation of operation, oxygen or some other suitable oxidizing agent is injected through tube 32, flared tube connection 25, hole 216 and angular orifice 27 impinging upon the spray of nitromethane and the colloidal suspension of catalyst in a non-detonat-ing fuel respectively as described above. The combined stream or spray is ignited by spark plug 6. After the motor reaches a temperature sufficient to permit continuous catalytic decomposition of the nitromethane or mixture of nitromethane and nitroethane, injection of the oxidizer may be discontinned.

When suitable precautions are taken to guard against overheating of the self-combustible fuel, the catalyst may be mixed with this fuel just before injection or may even be stored as a colloidal suspension in this fuel. When this is done care must be taken to guard against explosion.

FIG. 3 is a cutaway view of a jet motor showing the injector end. Such an injector may be used instead of the plug 7 of FIG. 2. With this there is utilized a catalyst in the form of a fluid which is in itself catalytic or which will break down in the motor to provide one or more types of catalytic materials. This avoids the use of a suspension of a solid material and of an injector thereof, and consequently there is no danger of a buildup of solid particles in the orifices and injector with consequent stoppage of the motor. Instead the catalyst is injected into the motor as a clear fluid.

In FIG. 3, part of a cylindrical jet motor 1 is shown containing a spark plug 6 in its upper portion and in its lower portion an injector 55 consisting of a pipe plug 57 having a flare tube connection 56 at its outer end. A nozzle 33 is provided in the wall of the motor 1 in line with the injector 55. This injector is set in such a way that any stream injected therethrough meets a counterstream injected through an injector through plug-shaped member 34. Injector plug screws into member 34 and is locked with nut 45, and has a flared tube connection in 7 its outside end. A concentric hole 36 passes through plug 35 and terminates in a hole 37 which is drilled normal to hole 36 in the cylindrical end of the injector. A groove 38 is machined around the surface of member 35 concentric with hole 37. A helical groove 39 around member 35 extends from groove 37 and terminates at the frusto conical cap 40. Cap 40 and the conical recess 41 and orifice 43 contained in member 34 form a frusto conical space 42 through which a single propellant may be injected into the combustion chamber 1.

In operation the nitroparafiin fuel is injected into the motor through tube 46, injector plug 35, and hole 43. Simultaneously through injector and nozzle 33 a fluid is injected in opposition to the stream of nitroparafiin fuel, which will act as a catalyst either of itself or after reaction in the motor. The advantage of injecting the catalyst fluid through in an opposite direction to the main propellant stream is obvious, since breakdown of such catalyst fiuid is necessary to obtain maximum catalytic activity. Such breakdown is brought about by the pickup of heat for evaporation and decomposition of the catalyst.

Initiation of decomposition may be accomplished by the injection of oxygen or any other suitable oxygen-bearing compound through tube 47, injector plug 25, hole 26, and angular orifice 27 impinging upon the stream of nitroparafiin fuel and the stream of the catalyst. The combined streams are ignited by spark plug 6.

Fluids suitable for catalysts may be liquid compounds, liquid solutions, gaseous compounds or gaseous mixtures. For example, liquid compounds may comprise CrO CI Mn O or Fe(CO) Liquid solutions will include solutions of Ce(NO in methanol or Ca(MnO in Water. Suitable gases may include Ni(CO) vapor or a mixture of Ni(CO) vapor with oxygen. All of these are fluids and may be easily broken down in the combustion chamber to give products which are catalytically active in the decomposition of suitable self-combustible fuels.

As an example of such a catalyst and of its behavior when injected into an operating jet thrust motor, consider the salt Ce(NO dissolved in methyl alcohol. The ordinary commercial form of Oe(NO containing some water of hydration, may be liquefied by methyl alcohol in the ratio of 5 grams of the salt to one cubic centimeter of alchol. The viscosity may be further reduced, if desired, by the addition of more solvent.

solution may be continuously injected into the motor at a rate normally only a few percent of that of the propellant. The injection is best made in the form of a fine spray in order to obtain maximum catalyst surface.

The first thing that occurs in the motor is the evaporation of the spray, yielding water vapor, methyl alcohol vapor, and Ce(NO in the form of fine particles. The water vapor cools the motor slightly without substantial effect on performance, and the methyl alcohol vapor burns and serves to some extent as additional fuel.

The Ce(NO decomposes according to the equation:

The CeO is a very active solid catalyst for the decomposition of nitroparafiins, acting by heterogeneous catalysis, while both the O and the N0 increase the rate of decomposition and flame speed of nitroparaflins, acting by homogeneous catalysis. Furthermore, the 0 and N0 help make up an oxygen deficiency in the nitroparaflins, thus increasing the available enthalpy and specific impulse. The

4 solid CeO particles will in part be ejected through the nozzle and in part adhere to the wall of the motor, where their catalytic activity will be continued.

In the use of the fluid catalysts, as in the case of the catalyst suspension, the fluid catalyst may be injected separately or in solution in the self-combustible propellant. If use in the combustible propellant suitable precautions must be taken to prevent overheating of the catalyst-containing propellant, in order to avoid explosion.

In some instances it may be desirable to continue the injection of a small stream of oxygen into the combustion chamber in order to obtain higher specific impulses and higher velocities. In such instances it is advantageous to continue the injection of the catalyst along with the small stream of oxygen as more rapid and complete combustion of the self-combustible fuel is thereby obtained.

We claim:

1. The method of opearting a jet motor having a combustion chamber and an exhaust nozzle from the chamber, which comprises injecting into the combustion chamber nitromethane and a catalyst selected from the group consisting of iron oxide, chromium oxide, chromium hydroxide, cerium oxide, and mixtures thereof and igniting the nitromethane in the chamber, thereby producing gases under pressure which are ejected out the exhaust nozzle.

2. The process of decomposing nitromethane which comprises heating nitromethane in the presence of a catalyst selected from the group consisting of iron oxide, chromium oxide, chromium hydroxide, cerium oxide, and mixtures thereof.

3. An improved fuel for use in a jet propulsion motor comprising nitromethane having suspended therein a catalyst comprising at least one substance selected from the group consisting of iron oxide, chromium oxide, chromium hydroxide, cerium oxide and mixtures thereof.

4. An improved fuel for use in a jet propulsion motor comprising a mixture ofnitromethane and nitroethane having suspended therein a catalyst comprising at least one substance selected from the group consisting of iron oxide, chromium oxide, chromium hydroxide, cerium oxide and mixtures thereof.

5. The process of decomposing a mixture of nitromethane and nitroethane which comprises heating the mixture in the presence of a catalyst selected from the group consisting of iron oxide, chromium oxide, chromium hydroxide, cerium oxide and mixtures thereof.

References Cited in the file of this patent UNITED STATES PATENTS 914,624 Winand Mar. 9, 1909 1,669,181 Walter et al. May 8, 1928 l,939,018 Odell Dec. 12, 1933 2,122,826 Peski July 5, 1938 2,231,605 Stephenson Feb. 11, 1941 2,233,620 Lippincott Mar. 4, 1941 2,310,306 Miller et a1. Feb. 9, 1943 2,317,557 Senkus Apr. 27, 1943 2,433,932 Stosick Jan. 6, 1948 2,433,943 Zwicky et a1. Jan. 6, 1948 FOREIGN PATENTS 384,079 France Jan. 25, 1908 459,924 Great Britain Jan. 18, 1937 OTHER REFERENCES Astronautics, issue of March 1936, pages 11-13. 

1. THE METHOD OF OPERATING A JET MOTOR HAVING A COMBUSTION CHAMBER AND AN EXHAUST NOZZLE FROM THE CHAMBER, WHICH COMPRISES INJECTING INTO THE COMBUSTION CHAMBER NITROMETHANE AND A CATALYST SELECTED FROM THE GROUP CONSISTING OF IRON OXIDE, CHROMIUM OXIDE, CHRONIUM HYDROXIDE, CERIUM OXIDE, AND MIXTURES THEREOF AND IGNITING THE NITROMETHANE IN THE CHAMBER, THEREBY PRODUCING GASES UNDER PRESSURE WHICH ARE EJECTED OUT THE EXHAUST NOZZLE. 